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Biomedical subjects

J C Elliott

Publications and source records attributed to J C Elliott.

At least 19 recordsLinked to original sources
PubMed1992

Acoustic microscope study of the elastic properties of fluorapatite and hydroxyapatite, tooth enamel and bone.

Measurements of Rayleigh velocity and attenuation were taken in single mineral crystals of hydroxyapatite and fluorapatite at angular intervals relative to their c axes, using an acoustic microscope. These results are compared with the values that were calculated using the elastic constants of apatite from Yoon and Newnham [(1969) Am. Miner. 54, 1193-1197.] and Katz and Ukraincik [(1971) J. Biomechanics 4, 221-227.]. The slowness curves of various wave modes are plotted and discussed in relation to cross-coupling effects that were found to cause instability in measurements of attenuation for the c axes direction. Velocity measurements were taken in specimens of tooth enamel and bone. Here comparisons are made with the values that were calculated by modelling the 'z' scan response of the microscope, using published data for the elastic and acoustic properties. Comparisons are also made with the measurements on single crystals, since apatite is a major component of enamel and bone.

Animals↗
PubMed1992

Evaluation of smear layers on serial sections of human dentin by means of electrochemical impedance measurements.

The alternating current impedance characteristics of a uni-directional porous glass membrane and serial sections of dentin from unerupted human third permanent molars (with and without smear layers) were measured. The membrane was equilibrated at 20 +/- 1 degrees C in a range of concentrations of unbuffered KCl, and the tooth sections were equilibrated in 0.1 mmol/L unbuffered KCl. Each section's impedance was measured for a 50-mV (rms) alternating potential difference applied over 1 Hz to 65 kHz. By means of complex non-linear least-squares regression analysis, the dc resistance of each specimen was determined. Scanning electron microscopy and subsequent image analysis enabled the cross-sectional area of the pores in the membrane and dentin tubule surface-openings to be measured. The results showed that the measured cross-sectional area of pores in the membrane was in good agreement with that calculated from the measured dc resistance and solution resistivity over the range of electrolyte concentrations. In dentin, the presence of smear layers on the cut surfaces increased the measured resistance. The resistance of the smear layer varied, suggesting that its thickness changed across the surface of the dentin. This was superimposed on regional variations in resistance of smear-free dentin which were found to be related to alterations in the number of tubules present and their cross-sectional area. The resistivities of the dentin tubule contents and smear layer material were generally lower than that of the hydrating electrolyte. It is postulated that this could be due to ions from partial dissolution of the mineral in the dentin.

Dentin↗
PubMed1992

Subsurface demineralization in dental enamel and other permeable solids during acid dissolution.

Subsurface demineralization of dental enamel during acid dissolution has been reported many times, but its cause remains obscure. At first, the phenomenon was thought to result from the physical structure of enamel. More recent studies have shown that subsurface demineralization occurs in other permeable solids, indicating that there must be more fundamental factors involved in this curious effect. In order for this phenomenon to be investigated, dissolution experiments were carried out by means of real-time scanning microradiography in various systems, including enamel, or aggregates of hydroxyapatite (calcium, strontium, or barium), or hydroxides (calcium or magnesium). These were chosen to discriminate between effects of structure and composition. It was found that it was not possible for the demineralization observed in these systems to be attributed to a common feature. From this, it is concluded that subsurface demineralization in enamel and other mineralized tissues should not be ascribed to a single cause.

Acetates↗
PubMed1991

Scanning and contact microradiographic study of the effect of degree of saturation on the rate of enamel demineralization.

The effect of degree of saturation with respect to hydroxyapatite (DSHA) on enamel section demineralization was studied by contact and scanning microradiography (CMR and SMR). Two aspects were studied: (1) the effect of different values of DSHA at constant pH, and (2) the effect of constant DSHA with variable pH. In the pH range (2.5-4.5) and time scale (0-120 h) studied, the DSHA was more important in determining the rate of enamel lesion progression than was the pH.

Adult↗
PubMed1990

Regional distribution of mineral and matrix in the femurs of rats flown on Cosmos 1887 biosatellite.

We combined biochemical measurements with novel techniques for image analysis in the rat femur to characterize the location and nature of the defect in mineralization known to occur in growing animals after spaceflight. Concentrations of mineral and osteocalcin were low in the distal half of the diaphysis and concentrations of collagen were low with evidence of increased synthesis in the proximal half of the diaphysis of the flight bones. X-ray microtomography provided semiquantitative data in computer-generated sections of whole wet bone that indicated a longitudinal gradient of decreasing mineralization toward the distal diaphysis, similar to the chemistry results. Analysis of embedded sections by backscattered electrons in a scanning electron microscope revealed distinct patterns of mineral distribution in the proximal, central, and distal regions of the diaphysis and also showed a net reduction in mineral levels toward the distal shaft. Increases in mineral density to higher fractions in controls were less in the flight bones at all three levels, with the most distal cross-sectional area most affected. The combined results from these novel techniques identified the areas of femoral diaphysis most vulnerable to the mineralization defect associated with spaceflight and/or the stress of landing.

Animals↗
PubMed1990

Electrochemical impedance characterization of human and bovine enamel.

The alternating current impedance characteristics of human and bovine enamel slices were measured in vitro. An electrochemical cell containing two platinum gauze electrodes and 0.01 mol/L KCl buffered to pH 7.4 at 20 degrees C was used. The electrodes were attached to a potentiostat that was connected to a microcomputer-controlled frequency-response analyzer. Measurements were made at discrete frequencies between 1 Hz and 65 kHz by application of a sinusoidal potential of 50 mV (rms) across the assembled cell. The impedance was calculated from the input potential and the resulting measured flow of current. For quantitative evaluation of these measurements, an equivalent circuit was postulated. It contained five passive electronic components and accurately modeled the different specimens. Values for individual electrical components in the equivalent circuit were estimated by complex non-linear least-squares regression analysis. This study demonstrated that it is possible to measure and quantitatively distinguish between the impedance characteristics of: permanent human, deciduous human, and bovine enamel, as well as the enamel from a variety of sites from human teeth, some of which had been extracted prior to being fully erupted. Proposals are made as to which physical properties in the specimens are modeled by individual components in the equivalent circuit.

Animals↗
PubMed1989

Three-dimensional X-ray microscopy with accurate registration of tomographic sections.

X-ray microtomography has been used to study the internal flaws and external shape of a 0.75 X 1 mm copper sulphate crystal at a resolution of 25 microns. The problems of accurate tomographic reconstruction and the subsequent registration of the reconstructed sections to give a complete 3-D image are considered when the position of the axis of rotation of the specimen varies slightly between projections.

Copper↗
PubMed1987

A performance comparison of select alkylbenzene and detergent based liquid scintillation cocktails.

Tritium was employed in the evaluation of performance characteristics for six commercially available cocktails represented by the manufacturers to possess favorable disposal characteristics. Unidentified alkylbenzene organic solvents and/or triton-like detergents form the basis for these cocktails, which were evaluated in large (20 mL) and mini (7 mL) glass and polyethylene vials. The cocktails showed higher backgrounds, lower unquenched efficiencies, and greater quench resistance to nitromethane than a reference toluene based preparation. Detergent based cocktails were difficult to dispense accurately, and resisted sample incorporation. One cocktail lacked stability in polyethylene vials.

Benzene Derivatives↗
PubMed1985

Infrared determination of the degree of substitution of hydroxyl by carbonate ions in human dental enamel.

About 11 +/- 1% of the carbonate ions in a human tooth enamel specimen (dense fraction, sp. g. greater than 2.95) were found to be in the A-sites, replacing hydroxyl ions. The determination was made with a difference infrared spectrometry technique utilizing both tooth enamel and a reconstituted biological apatite with a known amount of replacement of hydroxyl by carbonate ions.

Calcium Phosphates↗
PubMed1985

X-ray microscopy using computerized axial tomography.

Computerized axial tomography with MoK alpha X-radiation has been used to study a 0.8 X 0.8 mm column of human femoral bone at a resolution of 15 micron. This non-destructive X-ray microscopic technique allowed 'sections' to be made with 25 micron separation and the distribution of linear absorption coefficient in each section to be determined.

Bone and Bones↗